Contents

Executive Summary

The purpose of this project was to dissect the Black and Decker 4.5 Amp jigsaw and to identify the different processes of production and operation. This was accomplished through a dissection of the product and analyzing each part individually. These steps can be viewed in our Disassembly Procedure and After Disassembly sections. In total we have found 39 pieces to make up the saw, all with a great importance to proper functioning. The jig saw converted electrical energy to linear mechanical energy through a designated path. This process is explained in our Post Assembly Review section. There were no parts that could be left out of the product; however there are aspects that could be improved. These are discussed in our After Disassembly Assessment section.

Introduction

The Black and Decker 4.5 Amp jigsaw is a handheld power tool that is designed for light cutting through materials such as wood, plastic, and metal. Its small blade allows for cutting in tight spots and sharp corners.

Group members include:

Jonathan Mills

Michael DiGiovanni

Joshua Benson

Matt Bryden

Jason Bhatti

Dominic D'Costa

Before Disassembly Section

Purpose

The purpose of the product is to cut through wood, metal or plastic quickly and safely. The adjustable shoe plate allows for angled cuts and the jig saws compact design allows for easy maneuverability through sharp intricate cuts.

How it works

We assumed that an electric motor took in AC power to create rotational motion in a set of gears. Through an offset gear, rotational motion was converted to linear motion in order to drive the saw blade up and down.

Condition

The product worked great and had no evidence of prior use or disassembly. The input was AC power and the output was linear motion of the blade. It sounded like some type of electric motor was inside.

Parts

After inspection of the saw we assumed there to be approximately 30 parts.

Materials

We assumed there to be approximately 5 different types of materials used in the product. These included:

Plastic

Steel

Gel

Copper

Aluminum

Disassembly Procedure

Step #

Process

Tool Used

Level of Difficulty

Picture of step

1

Remove the Seven Philip screws from the rear casing with a medium size Phillips-head screw driver.

Remove two Phillips head screws from the power cord and remove the bracket

Phillips-head screw driver

easy

8

Remove trigger lock from casing then pull the spring and the spacers from the inside of the trigger lock

Hands

medium

9

Remove trigger from casing

Hands

easy

10

Remove power cord, wires, motor and all gear components from the casing as one piece

Hands

medium

11

Remove linear oscillator from motor assembly

Hands

easy

12

Remove two Allen wrench screws from the linear oscillator to release the blade holder

Allen wrench

Hard

13

Remove two steel guide supports and felt protection plate from the linear oscillator by sliding of the ends

Hands

easy

14

Take the blade holder and remove the plastic lever, then remove two springs from blade holder

Hands

Hard

15

Remove bushing from main steel gear

Hands

easy

16

Remove gear from ¼ inch plate by pulling gently

Hands

easy

17

Slide ¼ inch plate and the thin spacer from the motor mount

Hands

easy

18

Slide armature out of Slater

Hands

easy

After Disassembly

Part Table

Part #

Part Name

Quantity

Material

Manufacturing Process

Purpose

Picture

3D Drawing

1

Casing Screws

7

Steel

Extruded and machined

Hold casing together

2

Back Casing

1

ABS Plastic

Injection molded

Hold and protect components

3

Front Casing

1

ABS Plastic

Injection molded

Hold and protect components as well as secure motor, cord and blades

4

Power Cord

1

Plastic, copper wire and braded insulation

Copper wire is extruded, twisted and then wrapped with insulation and plastic coating

Supply AC power to the saw

5

Trigger Switch Assembly

1

Plastic, Copper, Steel and aluminum

Injection molded, extruded and assembled

To Convert AC to DC power and send it to motor in variable amounts

6

Lead Wires

2

Plastic and copper

Copper wire is extruded and coated with plastic insulation

To supply motor with electrical current

7

Stator

1

Steal, plastic, copper, metal, paper

Pressed, Injection molded, extruded, assembled

Creates magnetic field in order to spin the armature

8

Armature

1

Steel, copper, plastic

Pressed, extruded, machined, assembled

Creates rotational motion

9

Brushes

2

Plastic, carbon, copper

Injection molded case, extruded wire and spring

Change the polarity on the motor by rubbing against copper

10

Thin spacer plate

1

Steel

Stamped

Reduces wear on larger metal plate

11

1/4 inch metal spacer guide

1

Steel

Casted and machined

Guides gear movement

12

Oscillating gear

1

Steel

Machined

Start of rotational motion to linear motion

13

Bushing

1

Steel

Machined

Link between gear and linear oscillator

14

Guide support

2

Steel

Machined

Guides and supports linear oscillator

15

Felt piece

1

Felt

Cut

Dampen vibration and keep debris out of the saw

16

Linear oscillator

1

Steel

Machined

Oscillates vertically and holds the blade

17

Blade holder/changer

1

Steel and copper

Cast and stamped

Hold cutting blade

18

Blade holder spring

2

Steel

Extruded and wound

Supply pressure to blade to hold it in place

19

Lever

1

Plastic

Injected molded

Depress springs to allow for blade change

20

Blade guard

1

Plastic

Injection molded

Protects user from blade

21

Air duct

1

Plastic

Injection molded

Deflects air to blade in order to blow shavings away

22

Internal plastic screw gear

1

Plastic

Injection molded and machined threads

Tightens and loosens shoe plate

23

Shoe plate bolt

1

Steel

Cast and machined

Holds shoe plate in place

24

Saw blade guide

1

Steel

Pressed and machined roller

Guides and supports blade

25

Shoe Plate

1

Steel

Pressed

Keeps blade equidistant from cutting surface and supports saw

26

Air duct part 2

1

Plastic

Injection molded

Continues are deflection to blade for shaving removal

27

External thumb gear

1

Plastic

Injection molded

Provides user access to loosen or tighten shoe plate angle

28

Trigger lock

1

Plastic

Injection molded

Locks trigger on

29

Trigger lock spring

1

Steel

Extruded and wound

Keeps trigger lock in either on or off position

30

Trigger lock spacer

2

Plastic

Injection molded

Catch casing in order to hold trigger lock centered

31

Gel Max grip

1

Plastic and Gel

Filled and stamped

Provide soft grip for users hand

32

Power cord screws

2

Steel

Extruded and machined

Secure power cord bracket to front casing

33

Power cord bracket

1

Steel

Stamped

Hold down power cord

34

Power cord protector

1

Plastic

Injection molded

Protects power cord and keeps contaminates out of casing

35

Fan

1

Plastic

Injection molded

Keeps motor cool and directs air through air duct

36

Motor mount

1

Steel

Cast

Holds motor down and connects gears

37

Extra blade holder

1

Plastic

Injection Molded

Holds extra blades for easy access

38

Allen head screws

2

Steel

Extruded and machined

Hold blade holder to linear oscillator

39

Motor mount screw

1

Steel

Extruded and machined

Holds top of motor to front casing

After Disassembly Assessment

Materials

During the design process of the Black and Decker jigsaw, after each component has been designed to its working shape it must be analyzed so the proper material can be selected to create each part. Things that must be put into consideration are the various types of stresses and forces that are to be applied to each part. For the jigsaw there are five different materials that compose the entire powertool: ABS plastic, steel, copper, carbon, and the gel.

ABS plastic is used in parts such as the casing, shoe plate gears, and air ducts 1 and 2. This material was chosen for these parts because they experience little wear, high speeds, or forces. This material is also cost effective and ideal for the mass production of parts as the Black and Decker makes a large quantity of jigsaws each year. Everyone of these parts are injection molded which is a quick method of production.

Steel is used in components such as the gears, shoeplate, linear ocilator, and the 1/4" plate. This material was chosen because its level of hardness allows for a long lifespan of the product as all of these components experience a great deal of wear and tensions. The gears are constantly spinning at a high rpm and constantly rub against each other. If made out of a soft material the internal parts would last only a fraction of the time.

Copper was used in any part that needed to carry an electrical current such as the wires, coils in the stator and armature, and springs in the brushes. While being slightly costly copper has a very high conductivity and allows the electrical components to function properly.

Carbon was used in the brushes to pass current to the armature and alternate the polarity in the motor. This is what allows the motor to turn.

The "Gelmax" grip was made with gel to cushion the operators hand when the jigsaw is in use. This gel is ideal for this part because it freezes at very low temperatures which allows for the use of the saw outdoors during all seasons.

Improvements/Design Changes

1/4” plate has extra holes that are not needed. Machining could be cut down by eliminating these.

The gear has holes that are not needed which can be eliminated and cut down on production costs.

A stop could be incorporated into the casing so the armature is more easily placed into the correct spot into the stator. This would make the assembly easier and reduce the chance of rubbing in the motor.

Wires that connect the stator to the brushes could be shortened so they don’t have to be wrapped around the brushes. This would make assembly easier and cut down on the cost of the product.

In the jigsaw there are two different length screws, both with the same thread. If there was one size screw to fasten all parts, the assembly would be easier and the cost would be cut down.

Although all of the parts are necessary in the operation of the saw, two pieces of the assembly that could be combined are the air duct 1 and air duct 2 as this piece constantly falls apart upon reassembly. There is no need to separate these components as they would be stronger as one and not give the hassle when assembling the saw.

Gear Assembly

The components in the gear assembly fit together very easily and compiled completely by hand. The quarter inch plate acts as a spacer and a holder for the gears which slide into the alotted slots. These slots allow the gears to rotate freely in the given space. On the right side of the gear is an offset post that a bushing slides onto. This bushing is what sits in the linear oscillator and reduces friction while in operation. The linear oscillator is next slid onto the bushing and the guide supports are slid tho the ends of the oscillator. These are what holds the oscillator in place and protects the casing from wear.

Assembly Procedure Table

Step #

Process

Tool Used

Level of Difficult

1

Slide armature into Slater

Hands

easy

2

Slide thin spacer and then the 1/4 inch plate onto the motor mount

Hands

easy

3

Put steel gear back on to gear box by sliding the shaft into the motor mount make sure the gears line up

Hands

medium

4

Place the bushing back onto the gear

Hands

easy

5

Place the springs and the lever back onto the Blade holder

Hands

medium

6

Put the guide supports and felt protector plate back onto the oscillator

Hands

easy

7

Slide the blade holder onto to the linear oscillator and put in two Allen wrench screws to hold in place

Hands and Allen wrench

hard

8

Place linear oscillator onto the steel gear

Hands

medium

9

Carefully place the power cord motor and gear components back into the casing, realign motor to the grooves and motor mount to designated grooves to assure exact fit

Hands

hard

10

Push the brushes back into designated brackets and align wires to the grooves in the casing

Hands

hard

11

Assemble trigger lock and slide trigger lock and trigger into casing

Hands

medium

12

Place bracket for power cord into place and hold it in with two Phillips-head screws

Phillips-head screw driver

easy

13

Put Phillips-head screw into motor mount

Phillips-head screw driver

easy

14

Place the blade guide and bolt through shoe plate and attach internal gear screw to the bolt

Hands

medium

15

Place shoe plate assemble into casing

Hands

hard

16

Place external gear screw, Gel Max grip, blade guard back into the casing

Hands

easy

17

Take the two casings and put them together

Hands

medium

18

Insert 7 Phillips-head screws into the casing

Phillips-head screw driver

easy

Post Assembly Review

After it was reassembled the jig saw still functioned and sounded the same as it did when we had first gotten it and tested it out and it sounded and looked like it was functioning like nothing ever happened to it. It didn't show any signs of failure or overheating or binding of the gears.

The jig saw functions by converted AC power which is brought into the jig saw via the power cord to DC power. The power travels to the switch which is located in the handle of the jigsaw. The switch regulates the amount of electricity that travels to the motor which provides the variable speeds. The electricity travels to the motor and the motor creates a magnetic field from the current traveling through the copper coils. The magnetic field is located between the Slater and the Armature which creates the Armature to spin causing rotational energy. The rotational energy spins the gear which is connected to the linear oscillator which converts the energy into linear energy. The linear energy moves the blade in a linear motion resulting in a cutting action.

Some analysis procedures that could be performed to test the product would be:

Drop test to test the strength of the casing

Endurance test to test out the durability of the motor and the brushes

Test by cutting through different materials with different hardness to test motor's power

The disassembly and the assembly of the Black & Decker jigsaw were for the most part on the easy side for difficulty. The disassembly steps mirrored the assembly steps, every part came out just as easy as they went back in. The only steps that were really difficult would be getting the motor and the motor bracket to line up into their grooves